1. Field of the Invention
The present invention relates to a method of controlling a fuel cell system which has a fuel cell and an energy storage device, and which is capable of regenerating electric power.
2. Description of the Related Art
In a conventional technique, a fuel cell system for suppressing degradation of a fuel cell used in a fuel cell vehicle or the like is proposed, and in the fuel cell system, power generation is performed in a manner that the oxidation reduction electrical potential is avoided (U.S. Patent Application Publication No. 2009/0029197 (hereinafter referred to as “US 2009/0029197 A1”)). In the fuel cell system disclosed in US 2009/0029197 A1, even if electric power required by the system Wreq is increased gradually, the output voltage Vfc of the fuel cell is limited by the oxidation reduction potential Voxpt, and electric power corresponding to the limited voltage is compensated by a battery under control. Thereafter, even if it becomes unnecessary to perform power generation of the fuel cell, e.g., due to decrease in the opening degree of an accelerator pedal, the output voltage of the fuel cell is maintained at the oxidation reduction potential or less, and power generation is continued until the remaining battery level in the battery exceeds a predetermined value (abstract and FIG. 3).
Further, a fuel cell system aimed to effectively collect regenerative electric power has been developed (Japanese Laid-Open Patent Publication No. 2009-295516 (hereinafter referred to as “JP 2009-295516 A”)). An object of JP 2009-295516 A is to provide a fuel cell system which is capable of collecting regenerative electric power from a traction motor as much as possible in a power system using a fuel cell and a battery in combination to supply electric power to the traction motor (abstract). Therefore, in the fuel cell system 20 of JP 2009-295516 A, as the regenerative electric power increases, the lower limit reference value of an output range of the fuel cell 1 is lowered, whereby output electric power of the fuel cell 1 is controlled within the output range (claim 1).